The invention relates, generally, to a method of pouring predetermined quantitites of molten metal from a container through an inclined pour-out conduit having an inlet in the region of the bottom of the container and having an outlet at a level higher than the highest level to which molten metal is permitted to rise within the container, involving the controlled supply of pressurized gas into the interior of the container, the container being substantially gas-tightly sealed by means of a covering dome. More particularly, the invention relates to the pouring of predetermined quantities of molten metal in at least two successive pouring operations, with the molten metal level in the pour-out conduit being set to the same "starting level" at the start of each pouring operation by effecting a "starting pressure" build-up in the interior of the container, the starting level being beneath the level of the pouring opening but higher than the highest level to which molten metal is permitted to rise within the body of the container, with each pouring operation being initiated by superimposing upon the aforementioned starting pressure an additional "pouring pressure" which together add to form the total "feed pressure".
The invention also relates to an arrangement for performing the method.
When pouring molten metal from a container, for example from a foundry ladle or from a holding furnace, using pressurized gas, preferably pressurized air, to force the molten metal to leave the container, it is in general necessary that each pouring operation involve the pouring or dispensing of an exactly predetermined quantity of molten metal. In this connection, a particular problem resides in the fact that the upper surface of the molten metal descends inside the container during each pouring operation, resulting in a continuing increase in the static pressure difference inside the pour-out conduit between the level of the pouring opening and the level of the upper surface of the molten metal bath inside the container. If during a particular series of pouring operations the same quantity of molten metal is to be poured out during each successive pouring operation, then it is not enough to employ during each successive pouring operation the same feed pressure p.sub.f and the same so-called "pouring time" t.sub.g, i.e., the time during which the feed pressure p.sub.f is maintained during the pouring. Instead, if the values of p.sub.f and t.sub.g are kept constant during the series of pouring operations, the quantity of molten metal dispensed will decrease from one pouring operation to the next.
Experience has indicated that, to maintain constant the quantity of molten metal dispensed in successive pouring operations, the metal bath in the pour-out conduit must, prior to each pouring operation, be forced to rise up to a level below that of the pouring opening of the pour-out conduit but above the highest level to which the metal bath is permitted to rise in the interior of the container, i.e., must be forced up to the so-called starting level, by introducing pressurized gas into the interior of the container, i.e., into the space above the upper surface of the molten metal bath occupying the interior of the container. The gas pressure needed to establish this starting level is referred to herein as the starting pressure p.sub.v. The starting pressure p.sub.v increases during a series of pouring operations, from one pouring operation to the next, with the decrease, from one pouring operation to the next, of the quantity of metal in the container. After the establishment of the starting level, the dispensing of molten metal from the pouring opening of the pour-out conduit is effected by increasing the gas pressure in the interior of the container, as a result of which the metal bath level in the pour-out conduit rises up to the pouring level. To this end, the gas pressure in the interior of the container is increased from the starting pressure p.sub.v by addition of the so-called pouring pressure p.sub.g, to produce the feed pressure p.sub.f. Accordingly, at the start of each pouring operation p.sub.f =p.sub.v +p.sub.g.
With the known method the interior of the container, i.e., the space above the molten metal bath therein, is usually completely depressurized, so that atmospheric pressure prevails in the interior of the container. With this approach, prior to each pouring operation, the gas pressure must be raised from atmospheric pressure by the amount of the predetermined starting pressure. Between the individual pouring operations there are present undesirable dead times, not only in consequence of the complete collapse of the overpressure in the interior of the container, but also because the level of the upper surface of the metal bath in the pour-out conduit, on account of the large height difference corresponding to the large difference between atmospheric pressure and starting pressure, oscillates about the two corresponding levels, alternately rising above and falling below each of these two levels before finally assuming a steady level. Considerable time must pass before the liquid level in the pour-out conduit ceases to alternately rise and fall and finally assumes a steady level. If the liquid level is not given time enough to assume a steady level and if instead the next pouring operation is initiated before such steady level is assumed, the pouring operation will be very imprecise.
The known method of pouring predetermined amounts of molten metal by using pressurized gas in general does not take into account the collapse of the overpressure in the interior of the container attributable to gas leakages. As a result, it becomes impossible to precisely dispense predetermined quantities of molten metal, particularly when different quantities of metal are to be dispensed or when the dead times between the individual pouring operations are not of equal duration.
If using the known method the quantity of molten metal to be disposed is to be the same from one pouring operation to the next, then it is not possible to replenish the container with additional molten metal during the actual performance of a pouring operation. Instead, the container must be replenished during the pauses between successive pouring operations, which likewise leads to undesired dead times between the individual pouring operations.